1. Field of the Invention
The present invention relates generally to clutch control units for vehicles and, more particularly, to a clutch control unit capable of automatically connect or disconnect the clutch by learning.
2. Description of the Prior Art
FIG. 4 shows an automatic transmission including a conventional clutch control unit. A well-known parallel gear type transmission 1 is controlled by a transmission actuator 2 which consists of a select actuator shift actuator 2b. Both of the actuators 2a and 2b are driven by a hydraulic drive system 3 which consists of a tank 3a, a pump 3b, an accumulator 3c, and a hydraulic pressure switching electromagnetic valve (not shown) to control the transmission 1 via piston rods 2c and 2d. This control is made by the central processing unit (CPU) of a drive unit (D/U) 2e which in turn is controlled by a main control unit (C/U) 4 having a CPU, a read only memory (ROM), and a random access memory (RAM) through serial communications. A pair of potentiometers 2f and 2g are provided to detect the positions of the piston rods 2c and 2d, respectively. The actual position signals of the respective potentiometers 2c and 2d are fed back to the transmission drive unit 2e to control the gear positions so that they agree with the target position signals. An input shaft sensor 5a is provided to detect the number of revolutions v of an input shaft 1a of the transmission 1. A vehicle speed sensor 5b is provided to detect the number of revolutions V' of an output shaft lb of the transmission 1 or the vehicle speed. The outputs of the respective sensors 5a and 5b are inputted to the main control unit 4.
A clutch 6 is interlocked to the piston rod 7a of a clutch actuator 7 to make connection or disconnection. The hydraulic pressure is supplied to the clutch actuator 7 by the hydraulic drive system 3 to perform a feedback control by the CPU of the clutch drive unit 7b so that the position signal of the piston rod 7a detected by the potentiometer 7c agrees with the target position signal from the main control unit 4. The clutch drive unit 7b is also controlled by the main control unit through serial communications. An engine 8 has a control unit 8a which is controlled by the main control unit 4. An engine revolution sensor 9 is provided to detect the number of revolutions V of an output shaft 8b of the engine 8. The revolutions of the engine 8 are transmitted to an axle 10 via the clutch 6 and the transmission 1. The output of the engine revolution sensor 9 is inputted to the main control unit 4, into which signals from an acceleration pedal sensor 11, a brake pedal sensor 12, a key switch 13, an exhaust brake switch 14, and a gear position selector 15 are also inputted to control the transmission drive unit 2e, the clutch drive unit 7b, the engine control unit 9, a display panel 16, and a control unit 17a which controls a gear position display panel 17.
In this way, the main control unit 4 controls the clutch 6 and the transmission 1 according to the amount of pressing the acceleration pedal, the vehicle speed, and the shift position of the gear position selector. The gear position is controlled by the select actuator 2a and the shift actuator 2b corresponding to the shift of the gear position selector 15 in the select or shift direction from the neutral position N. That is, it is controlled into the first, second, third, or reverse position when the set position is "1", "2", "3" or "R". However, when the set position is "D4" or "D5" or automatic shift position, it is controlled according to the gearshift map based on the amount of pressing the acceleration pedal and the vehicle speed; i.e., automatic shift is made between the first and fourth gears at "D4" and between the second and fifth gears at "D5".
The control of connection or disconnection of the clutch 6 is made before and after the shift control by the main control unit 4 via the clutch drive unit 7b and the clutch actuator 7. This control is made based on the clutch connection characteristic obtained from learning activities made at a predetermined point of time.
FIG. 3(a) shows a learning activity. A learning starting point S has been stored in a memory of the main control unit 4. A half clutch point F is determined by moving the clutch 6 from the learning starting point S toward connection until the number of revolutions v detected by the input shaft sensor 5a becomes slightly greater than 0. Then, the clutch action starting point Q and the clutch connection completion point P are determined by taking predetermined offset values (operation distance) 1.sub.1 and 1.sub.2 from the half clutch point F in the directions of disconnection and connection, respectively. The clutch connection characteristic M is drawn from the half clutch point F, the clutch connection completion point P, and the clutch action starting point Q and stored in the memory. In the next learning activity, the previous clutch action starting point Q is taken as a present learning starting point S to start a learning activity similar to the above. By controlling the connection or disconnection of the clutch 6 according to the clutch connection characteristic M obtained from such learning activity, it is possible to reduce not only the wear of the clutch 6 but also the operational stroke of the clutch 6, thus making the shift operation faster.
With the conventional clutch control unit, the clutch action starting point Q, which is determined from the learning value stored in the memory of the main control unit, is taken as a learning starting point S to connect the clutch gradually, and the half clutch point F at which the input shaft of a transmission starts to rotate is taken as a learning point. However, when the clutch plate or actuator is replaced, the actual learning point can be far different from the learning value stored in the memory, and the clutch can have already been connected at the predetermined learning starting point S (clutch action starting point Q). As shown in FIG. 3(b), if the number of revolutions of the input shaft is shifted with respect to the clutch position, it is impossible to learn because the number of revolutions of the input shaft v.noteq.0 (rpm). Accordingly, extremely accurate positioning has been required for replacing the clutch plate or actuator.
Japanese Patent Application Kokai No. 60-34525 has proposed that clutch connection completion and connection starting points are determined by learning activities and added to the previous values to determine a new clutch operation range. However, it has had the same disadvantage as the above. In addition, the previous learning values always have a great influence so that a large number of learning cycles are required to provide an appropriate learning value.